1. Field of the Invention
The present invention relates generally to the field of hydrocarbon removal from hydrocarbon-carrier gas mixtures, and more particularly but not by way of limitation, to processes for the economical removal of hydrocarbon components from hydrocarbon-air mixtures and the enrichment of hydrocarbon product streams produced thereby for use as fuel or chemical feed stock.
2. Discussion
Many industrial operations have losses of hydrocarbon gases to the atmosphere. This venting represents valuable product losses as well as presenting serious contamination to the ambient atmosphere.
Should the vented hydrocarbon components be mixed with air, the possibility of ignition and resulting explosions is a very serious possibility. For example, mixtures of methane and air in which the methane concentration varies from about 4% by volume to about 14% by volume will explode if ignited. As a result of this explosion hazard, many hydrocarbon bearing streams are vented directly to the atmosphere rather than attempting to process the vapor stream for fear of ignition and resulting explosions.
A typical example is the loss of methane from coal mines. The methane exists in certain types of coal mines and is produced through drilled wells much as natural gas is produced through wells. These wells are drilled into the coal seams and the methane is extracted by application of vacuum to prevent the methane from flowing back into the coal mine where its presence would present a hazard to the workers of the mine. The methane content of the extracted gas from these wells, sometimes referred to as bore holes, may begin at nearly 100% by volume methane and reduce to less than 30% by volume methane as the mine is worked. The reason for this is that more air is drawn from the bore holes as the coal mine matures. This gas is used as fuel to power mining machines and it becomes difficult to use the gas as lean concentrations of methane are obtained.
Another coal mine operation in which methane is lost is through ventilation systems. A design of a typical ventilation system is that in which air is circulated through the operating coal mine in sufficient volume that the methane content of the air leaving the coal mine is frequently less than 1% by volume, which is below the lower flammability limit of approximately 4% by volume methane in air mentioned above. Even so, this can represent a significant loss of potential fuel, and depending upon regulatory conditions, the methane loss may represent serious contamination.